A training-induced increase in muscle capillarity appears to contribute to the reduced risk of cardiovascular disease and type two diabetes associated with aerobic fitness. Vascular endothelial growth factor (VEGF), a potent initiator of angiogenesis, is upregulated in cardiac and skeletal muscle by exercise. Estrogen also enhances VEGF expression, but the interactive effect of estrogen and exercise on VEGF in muscles has not been studied. The proposed study tests the theory that estrogen status affects exercise-induced upregulation of VEGF in cardiac and skeletal muscle. Four specific hypotheses will be addressed: 1. The levels of VEGF mRNA and protein are lower in the cardiac and skeletal muscles of estrogen-depleted, sedentary female rats than sedentary females rats with normal estrogen levels; 2. Exercise-induced upregulation of VEGF mRNA and protein are attenuated in the cardiac and skeletal muscles of estrogen-depleted female rats; 3. The levels of VEGF receptor (Fit-1 and FIk-1) proteins are attenuated in the cardiac and skeletal muscles of sedentary and exercised estrogen-depleted female rats; 4. Exogenous estrogen replacement restores exercise-induced VEGF mRNA and protein upregulation to control levels in the cardiac and skeletal muscles of estrogen-depleted female rats. These hypotheses will be tested using six groups of 6 mo. female Fischer 344 x Brown Norway rats (n=7 per group): sedentary control; sedentary ovariectomized (OVX), exercise control, exercise OVX, sedentary OVX with estrogen replacement, and exercise OVX with estrogen replacement. Rats in the exercise groups will be run once for 45 min at 20 m/min, 10 degree incline, an intensity previously shown to induce a 4 to 6-fold increase in VEGF mRNA in 6 mo. female Fischer 344 rats. VEGF mRNA levels in the heart and gastrocnemius will be analyzed by real-time PCR. VEGF and VEGF receptor protein levels will be assessed by Western blot. Analyses will be done using two-way ANOVA (exercise status, estrogen status). The results of this study will contribute to the assessment of the risk/benefit ratio for hormone replacement therapy, particularly in the context of those at risk for cardiovascular disease.